The lungs are separated from each other by the mediastinum, an area that contains the following: heart and its large vessels trachea (windpipe) esophagus thymus lymph nodes
Anatomy The right lung has three sections, called lobes. The left lung has two lobes. When we breathe, the air: enters the body through the nose or the mouth travels down the throat through the larynx (voice box) and trachea (windpipe) goes into the lungs through tubes called main-stem bronchi
– one main-stem bronchus leads to the right lung and one to the left lung – in the lungs, the main-stem bronchi divide into smaller bronchi – and then into even smaller tubes called bronchioles – bronchioles end in tiny air sacs called alveoli
Respiration Inspiration – Active process – by muscular action Contraction of diaphragm – Increase in vertical diameter Contraction of intercostals muscles – Elevation of ribs and sternum – Increase in antero-posterior and transverse diameter Expansion of lungs due to negative pressure – Air drawn inwards Expiration – Passive process – Elastic recoil of the lungs due to Relaxation of diaphragm and inter costal muscle. – Positive pressure created in lungs – Internal intercoastals, rectus abdominus, transverse abdominus, internal and external oblique. Control of Respiration – Control of Inspiration and Expiration by medulla oblongata
Lung Volumes The volume of air normally exhaled or inhaled with each breath during quiet breathing is called TIDAL VOLUME. (500ml) The additional volume of air that can be taken into the lungs beyond the normal tidal inhalation is called INSPIRATORY RESERVE VOLUME (3000ml) The additional volume of air that can be let out beyond the normal tidal exhalation is called EXPIRATORY RESERVE VOLUME (1100) The volume of air that remains in the lungs after a forceful expiratory effort is called RESIDUAL VOLUME (1200ml)
Lung Capacities The INSPIRATORY CAPACITY is the maximum amount of air that can be inhaled after a normal tidal exhalation (TV + IRV) (3500ml) FUNCTIONAL RESIDUAL CAPACITY is the amount of air remaining in the lungs at the end of normal tidal exhalation (ERV +RV) (2300ml) VITAL CPACITY is the maximum amount of air that can b e exhaled, following a maximum inhalation (IRV+TV+ERV) (4600ml) TOTAL LUNG CAPACITY is the sum of all the pulmonary volumes (5800ml)
Dead Spaces Some of the air the person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx, and trachea. This air is called dead space air because it is not useful for gas exchange. The normal dead space air in a young adult man is about 150ml. This increases slightly with age.
Ventilation Exchange of air between the lungs and the ambient air Tidal volume is 500ml Breathing frequency 15 th breaths/ min Total ventilation 7500ml/min Anatomical dead space 150ml Total ventilation 5250ml/min
Analysis of gases in respiration O 2 N 2 CO 2 Inspired air21%79%- Exhaled air16%79%5%
Lung Compliance The extent to which the lungs will expand for each unit increase in transpulmonary pressure is called the lung compliance. (transpulmonary pressure: difference between alveolar pressure and pleural pressure) Lung compliance: expandibility of lungs Lung elastic recoil: tends to collapse
Surface Tension Surfactant is fluid present in alveoli excreted by alveolar type 2 epithelial cells. is a complex mixture of several phospholipids, proteins and ions. The most important components are phospholipid dipalmitoyl phosphatidyl choline, surfactant apoproteins and calcium ions. Increases lung compliance, prevents collapse of alveoli and decreases the work of breathing.
Diffusion The passive tendency of molecules to move from an area of high concentration to an area of lower concentration Responsible for the passage of oxygen and carbon dioxide between the alveoli and pulmonary capillary blood.
Oxygen Transport Oxygen diffuses through the pulmonary alveolar capillary membrane and is then carried to the tissues in two forms: 1.Physically dissolve in plasma 2.Chemically bound to hemoglobin
Carbon Dioxide Transport Carbon dioxide diffuses through the tissue capillary membrane and is often carried to the lungs in three forms: 1.Physically dissolved 2.Bound to proteins as carbamino compounds 3.In bicarbonate form
Ventilation -Perfusion Three criteria must be satisfied Alveoli must be ventilated, Perfused, and Ventilation must match perfusion
Cardiac Output (CO) and Reserve Cardiac Output is the amount of blood pumped by each ventricle in one minute – CO is the product of heart rate (HR) and stroke volume (SV) HR is the number of heart beats per minute SV is the amount of blood pumped out by a ventricle with each beat Cardiac reserve is the difference between resting and maximal CO
Frank Starling Law of the Heart The more cardiac muscle is stretched within physiological limits, the more forcibly it will contract. Rubber band analogy Increasing volumes of blood in ventricles increase the stretch & thus the force generated by ventricular wall contraction. Greater stretch means more blood volume is pumped out, up to physical limits.
Frank Starling Law of the Heart Increased blood volume = increased stretch of myocardium = Increased force to pump blood out.